Stability Ball

Choose it Get on the ball to score flat abs in a flash. Crunches are up to 38 percent more effective on the inflatable orb, which comes in three sizes (55, 65 and 75 centimeters). For the right fit, your thighs should be parallel to the floor when seated.

Use it For proven gut shrinking, try the Rollout, says Michele Olson, Ph.D., professor of exercise science at Auburn Montgomery University. This stomach slimmer was rated most effective at firing ab muscles compared with six other ball moves, according to a study in the Journal of Orthopaedic & Sports Physical Therapy.

Rollout

Works: abs, arms, back

Kneel on floor behind ball. Place forearms on top of ball, hands clasped, to start. Contract abs and roll ball forward as far as possible without bending back or hunching shoulders (as shown). Hold for 2 counts, then return to start for 1 rep. Do 2 sets of 15 reps.

Medicine Ball

Choose it A soft, weighted medicine ball is as versatile as dumbbells but easier to hang on to, especially during dynamic moves that require twisting, swinging or throwing. (Ever try hurling a dumbbell? Don't!) The balls range in size from 2 to 30 pounds. Start with a 4-pounder; if you can fly through 12 reps unfazed, increase by 2-pound increments until you feel fatigued by the final rep, says Paul Katami, a trainer in Hollywood, California.

Use it The power-packed Suitcase Crunch does double duty, sculpting jiggle-free arms while taming your tummy.

Suitcase Crunch

Works: abs, shoulders, butt

Lie faceup with legs straight, arms extended behind head; hold ball with both hands above floor. Bring left knee toward chest as you lift upper back off floor and bring ball to left foot (as shown). Return to start. Repeat on opposite side for 1 rep. Do 2 sets of 12 reps.

Kettlebell

Choose it Quick physics: Because all of a kettlebell's weight (5 to 100-plus pounds) is in the cast-iron ball, not the handle, momentum is on your side during swinging moves, so you can likely hoist twice your typical heft. The quirky shape (teapot sans spout) also creates a long lever, providing unique resistance during static strength moves.

Use it The Gunslinger capitalizes on that leverage, leaving your biceps no choice but to get buff!

Gunslinger

Works: biceps

Stand with feet hip-width apart. Hold kettlebell in right hand at side. Keeping elbow at side, curl bell toward right shoulder until bottom of bell is pointed forward like a pistol (as shown). Lower to start. Do 12 reps. Repeat on opposite side.

BOSU

Choose it If you cut a stability ball in half and slapped a plastic base on it, you'd get the BOSU. Think of this balance trainer as a surfboard for landlubbers: Staying steady while standing on it activates your abs.

Use it Most people stand on the squishy side, but for an even more effective balance challenge, flip the BOSU over (it does mean "both sides up"), says Rich Barretta, who owns a private training studio in New York City. Now you're working to steady yourself and the BOSU, so during our tush-tightening, saddlebag-busting Side Kick, your abs are working…their butts off!

Side Kick

Works: abs, hips, butt

Stand with right foot centered on flat side of BOSU; step left foot back and to right on floor, arms out to sides at shoulder height. Balance on BOSU, swinging left foot out to side at hip level (as shown). Return to start. Do 10 reps. Switch sides; repeat.

Body Bar

Choose it Unlike a barbell, the weight on a Body Bar is evenly distributed along its 4-foot length, keeping you balanced. (Imagine you're a tightrope walker.) The bars are covered in rubber for a comfy grip and range in size from 4 to 36 pounds. Start with an intermediate-level 12-pound bar and go heavier or lighter from there, suggests Lashaun Dale, national creative manager for Equinox Fitness Clubs.

Use it Grip the bar during our bootylicious Pullover Bridge to fight arm flab and keep your body in proper alignment.

Pullover Bridge

Works: butt, arms, abs, thighs

Lie faceup with knees bent, feet flat, hips lifted; hold bar at waist with both hands to start. Lower hips to floor as you extend right leg, bend elbows and reach bar behind head (as shown). Return to start. Repeat on opposite side for 1 rep. Do 20 reps.

Step

Choose it This is no '80s flashback—the deck popular in high-impact aerobics classes is also a universal toning tool. Add risers to customize the height on this use-anywhere weight bench, Dale says.

Use it Who says you have to stay horizontal? Do the Decline Squat to downsize your butt and thighs while going easy on knees. Standing downhill helps perfect your form: You can sink deep into the squat without bringing knees too far over ankles.

Decline Squat

Works: abs, butt, thighs

Put three risers under one side of deck. Stand facing downhill, arms extended at shoulder height. Squat, then move right heel down step, toes up (as shown). Stand, extending right leg forward at hip height, bringing arms behind you. Return to start. Repeat on opposite side for 1 rep. Do 2 sets of 12 reps.

Foam Roller

Choose it Foam tubes come in 12-inch and 3-foot sizes and are generally used for rolling out tight, achy muscles, especially in the quads, hamstrings and calves. The fancy name for the technique is self-myofascial release—it's basically a sports massage minus the masseuse.

Use it The roller also has your back: Lying on it during the Treasure Chest releases tension in the muscles around your spine and forces you to balance, for firmer abs, says trainer DeAnna Bellamy, a corrective exercise specialist and owner of Body Revolution in Chicago.

Yoga Block

Choose it Not-so-flexible yogis lean on these foam blocks to maintain proper alignment during poses or sit on them for bonus back support.

Use it In the Serving Tray, the tone-up toy hangs in the balance, and keeping it stable helps to shrink your stomach as you lean your legs, says Kristin McGee, a yoga and pilates instructor in New York City.

Trampoline

Choose it Hopping on a mini-trampoline, also known as an urban rebounder­, is 68 percent more effective than running on a treadmill at a similar heart rate and oxygen intake, a NASA study finds. You can jump off the jiggle and go easy on your joints.

Use it There's no bouncing but plenty of benefit with the Trampoline Jackknife. The rebounder's unstable surface recruits even your deepest ab muscles, says fitness expert Jonathan Roche, who developed a trampoline workout system for Gaiam.